1. Field of the Invention
This invention relates to electrodeless discharge lamps (EDL's) of the type employed for spectrophotometric analysis, particularly in atomic absorption and atomic fluorescence spectrophotometry, and more specifically to lamps and methods of fabricating lamps for use as mercury spectral line sources.
2. Description of the Prior Art
The advantages of EDL's over other spectral sources, e.g., hollow cathode lamps, in terms of attainable detection limits for some elements are well known and, consequently, there has been considerable activity in recent years directed toward the development and utilization of EDL's where hollow cathode lamps have previously been employed.
The general requirements for EDL's are also well known: good stability, high intensity, and long life. The realization of these requirements, however, has been more difficult for some elements than others and, among the elements which have presented particular problems is mercury.
A resume of past efforts in the construction and operation of EDL's is presented in a paper entitled, "The Preparation and Operation of Electrodeless Discharge Lamps - A Critical Review" by J. P. S. Haarsma, G. J. DeJong, and J. Agterdenbos, published in Spectrochimica Acta, Volume 29B, pages 1 to 18. From this publication, it will be noted that, for the most part, mercury EDL's have been fabricated using elemental mercury rather than mercury compounds. Mercury compounds, e.g., mercury iodide, and mercury amalgams have also been employed. None of these have produced entirely satisfactory results, tending to give too intense an output or, where sufficient material is introduced to lower intensity, short life has resulted.